Experience: Differences between 1Z and AHU

Hi.

Today, I had the opportunity to take a closer look at a Golf 3 TDI AHU (early 1997). It has 150,000 km on the clock, which is the same as my 12/1995 model.

It does NOT make a clicking sound from the wastegate valve when the engine is off. Obviously, this is one of the differences between the engine control unit (ECU) used here, which is part number 028 906 021 GG, and my 1Z model, which has part number 028 906 021 AF.

In addition, the AHU model, like the AFN, features a long, flexible pipe with an extra double rubber support in front of the catalytic converter, which significantly dampens the vibrations of the exhaust system, especially when the exhaust is hanging freely by 1 to 1.5 meters.

The AHU (auxiliary heating unit) also exhibits a drop in airflow above 3000 RPM, similar to what I observed in my 1Z engine, but not as pronounced. "It's interesting that the target value at full load differs: 1Z is 847.9 mg/H, while AHU is 850 mg/H (but the actual output only reaches a maximum of 847.9)."
Both have the Pierburg mass airflow sensor.

Ulfs DZ-Test (presumably referring to a "door zone" or similar test) yielded a value of 9.4 seconds for the AHU (likely an abbreviation for a specific system or component). This is in comparison to my result of 8.6 seconds, which was obtained under different conditions: there was one more person in the car, it was warmer (approximately 8 degrees Celsius instead of -3 degrees Celsius), and the humidity was higher.

The Russian border was always just above the torque limit.

I hope I haven't violated any rules, as this isn't a direct question.
However, the difference between the 1Z and AHU engines has been asked about quite a few times already...

Greetings.
martin

Hello Martin,

Quote:

In addition, the AHU has the long flexible pipe (like the AFN) with the additional double rubber support in front of the catalytic converter,

Be careful, my AFN also has the "old" version with a free hanging length of 1.5 meters.
The exhaust system produces unpleasant rumbling vibrations just above the low-end RPM.
That's very annoying because it's a frequently used RPM range in the city.
Do you have any more information about when the improved version might have been installed in the G3? I doubt it's in the Passat, as that model was quite quickly replaced by the 3B.

Best regards,
ALbrecht.

Oops, an AFN with the drone version??

I've never seen that before... (and according to a "reliable source," it doesn't exist ).

I was incredibly frustrated and angry yesterday when I saw the AHU.

It seems to be almost a 1:1 replacement for a 1Z, and I had the catalytic converter and flex pipe replaced six months ago for 700 EUR because the flex pipe was loose (with almost no change in noise ).

It's possible that the AHU support bracket fits my 1Z, but the VW staff were too incompetent to check. They asked their computer, which said "drone version," so they just used that one, even though there might be a better option.

"As far as I know, the AFN engine has a different exhaust manifold flange, so there probably are even more exhaust pipe versions than I thought."

1Z Droehn
AHU support.
AFN Droeh.
AFN Support.

It's a shame that the Dron version has a very short flexible tube; otherwise, I would try combining it with the 1Z support and retrofitting the support.

Hi,

"You're talking about the roaring sound. I've personally heard a TDI (ALH) engine that had nothing but a straight pipe from the turbocharger all the way to the exhaust system." No flex shafts, no catalytic converters, no mufflers.
That was, in all seriousness, the quietest diesel engine I have ever heard, or rather, not heard. (It was audible, but much quieter than all the other diesel engines I have heard before.

The turbo was whistling extremely loudly due to the missing flexible coupling.
Just mentioning this for informational purposes, based on my experience!


Greetings.
Thomas.

Hello Albrecht,

Be careful, my AFN also has the 'old' version with 1.5 meters of free hanging space.

The 1Z engine had a catalytic converter with a flange attached, do you have that as well?

Hello.
Wolfgang.

Quote:

Didn't the 1Z have a catalytic converter with a flange on it? Do you have that too?

NO, not all 1Z models had it.

Mine came from the factory with the flex pipe and catalytic converter as a single unit.

Now, after the swap, it's separated (with this 3-bolt flange).

If I had already had the flange installed from the factory, I could have saved the 300 EUR for the catalytic converter.

m;

Hello Martin,

Okay, I learned something new again. But did the AFN (Armed Forces Network) never have a version of 'Kat' with a flange?
I'm just asking because I installed one in my AFN, simply because it's so convenient. I hope this doesn't cause any problems. The external dimensions are the same.

Hello.
Wolfgang.
T3 Syncro 16 with AFN engine.

PS: Do you still need the diesel fuel supply line?

According to. The "Teile Katalog" (parts catalog) did not include information about AFN and AHU engines with a modified catalytic converter.

But according to the parts catalog, they always have the support, and here in the forum, there are AFNs without the support, as mentioned above .

m;

Hello,

I've checked again. It's true that in the G3 model range, the AFN engine and, within the context of model updates, the 90 hp variants are the most common.
In the Passat 35i, which is essentially the same, this support doesn't exist at all .
The question is whether the throbbing would disappear if I used a brace .

Best regards,
Albrecht.

Quote:

As part of the model update, the 90 horsepower variants

Are you referring to the difference between 1Z and AHU?
So, that's exactly what I also discovered.

m

Hi.

Since you're investigating the exhaust noise here, I wanted to ask if it only occurs at a specific RPM, or if it's present across a whole range?
Usually, people talk about resonance occurring at just above LL, but in my case, it's booming all the way up to around 1600 RPM.

g.
Jan.


G3, 1Z, 1994, leaky flexible pipe.

Hello Jan,

My resonant frequency is between 1100 and 1200 RPM. A colleague recently installed a new center muffler and managed to get it aligned properly, so it turned out quite well.
As long as my exhaust (which is still the original system) is leak-free, I won't be modifying it.

Best regards,
Albrecht.

I'm hearing a very pronounced buzzing sound at 1400 RPM.

Initially, I suspected the MSD (module spark distributor) was the problem - new.

Then it was clear that it wasn't him, but the flexible pipe had a slight amount of play - the flexible pipe and catalytic converter were replaced.

Still not significantly better.

After I realigned the exhaust, it at least now sparks somewhere every time I start and stop the engine .

What really bothers me is that the car is noticeably louder in warm weather. It's as if the bodywork is too soft and is vibrating along with it. When it's cold, it's noticeably quieter (probably because it's more solid)!?

Is this a G3 Variant 12/95?

m

Okay, in my case, the roaring sound starts at idle and continues all the way up to 1600 RPM. Since I can hear the turbo whistling, my flex pipe is probably damaged (because I can't find any leaks in the pressure lines). However, I suspect the idle speed control system is more likely to be the cause of the excessive noise, as my auxiliary belt is vibrating significantly (probably due to a faulty vibration damper), and there's also a noticeable amount of adjustment needed for the idle speed of individual cylinders when using VAG-Com.
In this forum, it has been speculated before that a vibration damper that is not perfectly centered might potentially interfere with the idle speed control.
Of course, I have no proof that this is actually possible, but if it were, then it could potentially be the case to some extent for some of you . The speed limiting function is only active up to 1600 revolutions per minute.
Or am I completely wrong?

Best regards from Jan.